Document scanners are known in which the document transport is driven in stepwise fashion by a stepping motor. In these prior art systems, the scanner scans while the document is at rest. It is also known in the prior art to continually scan a document and discard those scans which occurred while the document was in stepping motion, and to discard extra scans which occurred while the document was at rest but which scans were redundant.
There exists a need in the prior art to provide a method of synchronizing the scans of a document to the motion of the document being scanned without introducing distortion of the image being scanned when the document drive motor speed varies due to varying friction.
There exists a further need in the prior art to provide a method of synchronizing the scans of a document to the motion of the document even as the document is brought to rest in a continuous nonincremental motion when the data processing and data compression circuits receiving the data from the scanner can not keep up with the data rate from the scanner.